Battery charger problem

[NgtvNrg]

I have a 2 bank on board charger (one bank hooked to deep cycle trolling motor battery and one to cranking battery) that I believe might have a problem. Normally I can plug it in when I get home and the batteries show to be charged by morning. Now I have had it plugged in for 2 days and it shows that it is still charging the batteries. I have already checked and replaced all the connections. Is there a way to test the charger? Also do I really need to have a charger hooked up to the cranking battery since the motor should recharge it while running?

 

[wire2]

Re: Battery charger problem

If your alternator and starting battery are ok, no, you won't need to charge it between trips.
What's the voltage on the trolling battery on charge?
Without charger?
Do you get a spark when you first clip on the charger?

 

[Boatist]

Re: Battery charger problem

What size battery do you have and what is the amp output of the charger?
A big trolling motor battery charged with a low amp charger like 6 amps can take several days. Check the battery voltage with the charger OFF.
Then check it with the charger ON. Note both voltages then check a day later. If Battery has been discharged more than 50 percent for any time it could now be defective.
You should charge both batteries at least one time a month in summer and in winter at least every two month if you want them to last 6 or 7 years. Also do not discharge starting battery below 80 percent and do not discharge Deep cycle below 50 percent. Then fully recharge as soon as possible for long life.

 

[jtexas]

Re: Battery charger problem

Take the battery to a car parts store, most will load test 'em for free - then you'll know if the battery or the charger's gone bad.

 

[NgtvNrg]

Re: Battery charger problem

Bought a digital multimeter to check it out. The cranking battery is at 11.88v with the charger off and 11.9v with it plugged in. The trolling motor is at 11.74v with the charger off and 11.76v with it plugged in. I am unsure of the amp output of the charger. The cranking battery is only 3 months old and is a has 1000 cranking amps. The trolling battery is a 24dc and is over a year old. I have charged them many times before and it has never taken longer than overnight.

 

[wire2]

Re: Battery charger problem

Your charger is not working.

There's maybe a few milliamps of current there to raise the battery voltage by so little. Put the charger leads to a headlamp or a 12v motor and see if it will run it. What's the voltage? A 60 watt headlamp bulb will draw 5 amps at 12 v.

I expect the charger uses older style (read; cheap) selenium rectifier plates rather than silicon diodes. They're notorious for failing. I've resurrected many chargers by converting to diodes.

 

[wire2]

Re: Battery charger problem

The trolling motor is at 11.74v with the charger off and 11.76v with it plugged in............
The trolling battery is a 24dc and is over a year old. I have charged them many times before and it has never taken longer than overnight.

Wait a minute, trolling battery is 24v? And you're charging it with a 12v charger, getting 11.76v?

One of those numbers isn't right.

 

[NgtvNrg]

Re: Battery charger problem

Wait a minute, trolling battery is 24v? And you're charging it with a 12v charger, getting 11.76v?

One of those numbers isn't right.

No it is a 12v battery, 24dc was the model# (not sure why I typed that), it is 140 reserve capacity and 100 amp hours.
The charger is an older model from a company that I believe is no longer in business (BattCat by Galvanix)

 

[Boatist]

Re: Battery charger problem

Well if your meter is accurite at all then both your batteries are way under charged. The Battery voltage should be 12.6 Volts in 70 to 80 degree temperatures.

Check your car battery and see if it is 12.6 volts before starting and 13.8 to 14.8 after starting. If it is then I would go buy a good smart charger of at least 15 amps or a on board charger for two banks of at least 10 amps each bank.

Even a 10 amp charger will take almost 24 hours to fully charge a group 24 deep cycle that is discharged as much as yours.

 

[jtexas]

Re: Battery charger problem

with the charger on, battery voltage should be over 14. the charger's toast.

 

[NgtvNrg]

Re: Battery charger problem

Ok, I'm going to get a new on board charger. Is Guest a good brand? Also is there a way I can check and see if my motor is charging the batteries while running? I'm concerned because I thought the cranking battery should have had more of a charge then it did.

 

[wire2]

Re: Battery charger problem

....Also is there a way I can check and see if my motor is charging the batteries while running? I'm concerned because I thought the cranking battery should have had more of a charge than it did.

Use your new meter to check the battery voltage with engine off, at idle and at 1000 rpm+.
Should be ~12v, ~13v and ~14v respectively.

 

[jtexas]

Re: Battery charger problem

with the charger on, battery voltage should be over 14. the charger's toast.

sorry, not specific enough - while the charger's charging a discharged battery it should at least start at over 14, may decline as charging progresses depending on the charging algorithm of the charger; might be a bit less when the charger goes to "float mode", if equipped.

 

[wire2]

Re: Battery charger problem

sorry, not specific enough - while the charger's charging a discharged battery it should at least start at over 14, may decline as charging progresses depending on the charging algorithm of the charger; might be a bit less when the charger goes to "float mode", if equipped.

Well, that's not really how it works either.
A standard battery charger consists of a step down transformer (115 to 24v ac) and a pair of diodes forming a center-tap full wave rectifier. The RMS output is 12 vdc but the peaks are 37.5% higher.

Connecting it to a dead or low battery results in high current. That means more losses in the transformer windings, rectifier, and output leads, so less voltage left over for the battery. It can't instantly bring the battery up to 14 volts.

I believe you're confusing voltage with current.

A low battery will start charging at high current, and lower voltage (because of the losses).
As the battery voltage approaches charger output, current will drop off, (less losses) and volts go up.